1. Technical Field
This invention relates generally to conveyors such as those used to convey articles toward a label applicator, and more particularly to a feedscrew system for controlling the movement of articles along the conveyor.
2. Background Information
Some feedscrew systems control the movement of articles along a conveyor in order to maintain the spacing desired for subsequent processing. In the case of label application, for example, the articles move along the conveyor into the entrance end of a pair of parallel feedscrews that are located above the conveyor in a position ahead of a label applicator. As the feedscrews rotate, they capture the articles in the valleys of the two feedscrew threads so that the articles leave the exit end of the feedscrews with spacing that conforms to the threads, just right for the label applicator.
However, there are certain problems with existing feedscrew systems that need to be overcome, such as the ability of the feedscrew threads to damage articles as the articles pass into the entrance end. Such damage can occur when one of the articles reaches the entrance end at a time that results in it becoming trapped between crests of the feedscrew threads instead of being captured in the valleys. When that occurs, the crests can compress the article sufficiently to damage it.
That problem can be reduced by jam-feeding the feedscrews (i.e., maintaining a line of abutting articles at the entrance to the feedscrews). Doing that helps because there are always articles ready to enter the feedscrews and the article that was the last to enter the entrance of the feedscrews holds back the article that is next in line to enter in such a way that it will not become trapped between the crests. However, a gap in the line of articles being supplied to the feedscrews can frustrate jam-feeding attempts so that the threat of damage remains.
Gaps can occur simply because the labeling rate is a little faster than the supply rate or for various other reasons associated with operation of the source of articles, the gaps sometimes being managed by blocking the movement of articles toward the entrance end of the feedscrews whenever a gap is sensed. Some sort of restraining mechanism may be activated for that purpose to act as a dam across the conveyor, and as soon as the articles catch up so that a jam-feed condition is restored, the dam is removed to unblock movement so that the articles can once again enter the feedscrews.
However, when using the damming technique, movement must be unblocked at just the right time so that movement of the first article is properly synchronized with feedscrew rotation. Otherwise the first article may arrive at the entrance end at just the right time to be caught between the crests and, in the case of various containers such as cans and bottles of liquid, even burst by the compression action of the crests. In addition to less efficient processing, that can cause damage to the feedscrew system and the conveyor system as well as injury to attending personnel. Consequently, it is desirable to have a feedscrew system that better alleviates those concerns.